The invention relates to a suction belt conveyor for a sheet processing machine, particularly a printing machine, with an operationally revolving suction belt as well as a delivery for a sheet processing machine, particularly a printing machine, with a sheet brake formed by suction belt conveyors.
A suction belt conveyor of the foregoing general type and with diverse realizable transport tasks have become known heretofore, for example, from the published German Patent Document DE 197 12 690 A1. A preferred application area is the delay of the stacking or depositing speed of the sheets running through the printing machine to a speed at which the sheets finally encounter stops that assist in forming sheet piles.
For example, in such an application, the suction belt revolves in a manner that each sheet transported to the suction belt is taken up without relative speed with respect to the belt speed, and that the belt subsequently delays the sheet to the depositing or stacking speed. The speed with which the sheets are processable is therefore primarily dependent upon how fast the sheets can be slowed down to the depositing or stacking speed thereof, i.e., high processing speeds require brief sharp delays of the sheets by the suction belt conveyors used for this purpose. Driving the suction belts in such conveyors with corresponding periodically changed speeds is realizable with suitable drive motors, but powerful friction forces must be available between the sheets and the suction belts for transmitting the correspondingly long delays to any of the sheets.
With respect to the most different characteristics of the sheets to be delayed, such as the coarseness or roughness of the sheets to be delayed and the available suitable materials for constructing the suction belt, there are certain limits in the selection of the highest possible coefficient of friction in the pairing of a sheet and a suction belt, so that a strongest possible normal force must exist for creating the high friction forces between the sheet and the suction belt. This requires a highest possible negative pressure or vacuum acting in largest possible suction openings of the suction belt, which can, however, result in markings being formed on the sheets by the rims of the suction openings.
It is accordingly an object of the invention to provide a suction belt conveyor for a sheet processing machine of the foregoing general type which is constructed so that high friction forces can be transmitted to the sheets and yet the sheets remain as unblemished as possible.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a suction belt conveyor for a sheet processing machine, comprising an operationally revolving endless suction belt having, at an outer side thereof a filigree structure formed by indentations, the suction belt being formed with penetrating bores terminating in the indentations.
In accordance with a second aspect of the invention, there is provided a suction belt conveyor for a sheet processing machine, comprising an operationally revolving endless suction belt formed with pores distributed in longitudinal and transverse directions of the suction belt, so that the suction belt is air permeable.
In accordance with another feature of the invention, the suction belt comprises an outer layer and an inner layer.
In accordance with a further feature of the invention, the suction belt has a transport strand and is operationally slidable by an inner side of the transport strand along a support, the transport strand having an outer side for exerting a higher friction force on a transported sheet than the inner side of the transport strand exerts upon the support when a given normal force acts upon the transport strand.
In accordance with an added feature of the invention, the suction belt is formed with parting lines extending substantially crosswise to the longitudinal direction of the suction belt starting from the outer side thereof, the parting lines extending in a direction towards the inner side of the suction belt.
In accordance with an additional feature of the invention, the suction belt conveyor includes a drive wheel, the suction belt having a form locking connection with the drive wheel at least at one edge of the suction belt.
In accordance with yet another feature of the invention, the suction belt, in supplied condition thereof, has a cross section extending in such a manner that an inner side and the outer side of the suction belt have a smaller extension along the longitudinal center thereof than at the edges thereof.
In accordance with a third aspect of the invention, there is provided a delivery of a sheet processing machine, comprising a sheet brake formed by a plurality of suction belt conveyors having at least one of the foregoing features.
In accordance with a concomitant feature of the invention, the sheet processing machine is a printing machine.
Thus, in a first variation of the invention, the suction belt has on the outer side thereof a filigree structure in the form of indentations, and the suction belt is formed with bores terminating in the indentations. In a second variation, the suction belt is formed as an air permeable belt with pores distributed lengthwise and crosswise.
In an advantageous embodiment, the suction belt has an outer layer and an inner layer.
Preferably the outer layer is formed of a material that generates the highest possible friction coefficient in the pairing of sheet and suction belt. In contrast, the inner layer is preferably formed by a material that can slide with as little friction as possible over the support supporting a transport strand formed by the suction belt and effecting the conveyance of the sheets. Such support has become known heretofore, for example, from the published German Patent Document DE 196 49 824 A1; it has at least one suction opening facing the conveyor strand and extends longitudinally along the conveyor strand. A given vacuum can be generated by a negative pressure or vacuum generator to penetrate the suction belt and to press the transmitted sheet by suction against the transport strand at the outer side of the outer layer. The normal force between the respective sheet and the transport strand as well as between the transport strand and the support causes a slight friction between the support and the transport strand due to appropriately selected materials of the inner layer; it also fosters an extension of the life of the suction belt.
The construction of the suction belt formed of individual layers provides also the advantage that the material of the outer layer does not have to be selected with attention to a given tensile strength. Tensile strength is required of the suction belt when it has to be accelerated again after it has released each sheet that has been slowed down to stacking or depositing speed.
This extends the possibilities for forming the outer layer of a material that generates a friction coefficient as high as possible in the pairing of sheet and transport strand.
In such a construction of the suction belt, the cross section height is possibly over-dimensioned with respect to the tensile strength of the suction belt. This is, however, to the benefit of the arrangement of the filigree structure formed by indentations on the outer side of the suction belt.
A further embodiment of the suction belt formed of an outer and an inner layer provides for parting lines or seams extending substantially perpendicularly to the length of the suction belt and starting at this outer side. These parting lines extend to the inner side of the suction belt. This prevents, in a simple manner, the generation of unnecessarily high tensions for the intended purpose of the suction belt; otherwise such tensions can arise when the suction belt is guided tautly over reversing devices. The parting lines also reduce an otherwise higher force for stretching the suction belt and also the corresponding higher inert forces in the event that the suction belt winds around the reversing rolls with pivot bearings.
In addition, at least one marginal edge of the suction belt is preferably formlocked and connected to a drive wheel. The formlocking connection permits an exact coordination of the speed behavior comprising the suction belt delay and acceleration phases to momentary turning positions of, for example, a cylinder carrying one of the sheets within the sheet processing machine.
In a preferred embodiment, the formlocking action connection is formed like a synchronous belt drive, while another preferred embodiment accomplishes the connection with a pin wheel gear. The limitation of the formlocking action connection to at least one of the lateral wheels of the suction belt creates a further advantage insofar as the suction belt can be guided over a support described hereinabove via a width extension at least in a marginal area of the suction belt while it is in complete contact with that support. The support does not support its marginal area. Despite the formlocking action connection especially in the manner of a synchronous belt drive, at least one suction opening of the support does not communicate with the surroundings via tooth gaps in the suction belt. Otherwise this would have the consequence that at least one suction opening of the support would suck inleaked air by reducing the suction effect directed to the sheets due to a given suction force of a negative pressure or vacuum generator connected with the suction opening. Therefore, a negative pressure or vacuum generator with higher suction capacity would be needed for generating a given suction effect. The limitation of the formlocking action connection to at least one of the side edges of the suction belt results, therefore, in a reduction of the otherwise necessary energy consumption.
Another preferred embodiment provides for the new suction belt cross section to extends in a way that the inner side and the outer side of the suction belt are smaller in the center thereof than at the edges thereof.
If a suction belt of this type is wound around reversing devices acting on the side edges, after the side edges are stretched, and if the transport strand is guided over the above support, the suction belt assumes an altered cross section course along the support in a way that the inner surface of the suction belt aligns itself with an elastic deformation to the straight course of the support which runs perpendicularly to the transport strand and slides over the support with a given normal force exerted on the support. The support has a straight support surface and is arranged in a manner that it supports the inner surface of the suction belt up to the vicinity of the side edges. This results in a desired complete contact of the transport strand with the support without any need for an additional stretching of the suction belt as is common with traditional suction belts.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a suction belt conveyer for a sheet processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: